Chemical alterations in the brain hint at whether loss of smell will return post-COVID
Experts have identified changes in part of the brain they believe are responsible for lingering anosmia triggered by COVID-19 infections.
Using proton magnetic resonance spectroscopy imaging (MRS), researchers homed in on altered neurochemical patterns in the orbitofrontal cortex (OFC) of the brains of patients who have not yet fully recovered their sense of smell since being infected with COVID. Some of the findings could be used to elucidate whether individuals will recover their sense of smell over time, authors of a new research paper suggested.
“Although the exact mechanisms underlying this persistent anosmia remain unclear, emerging evidence suggests that dysfunction in the central nervous system may play a crucial role,” Shadman Nemati, with the Department of Otolaryngology and Head and Neck Surgery at the Otorhinolaryngology Research Center in Iran, and colleagues explained. “Olfactory processing begins with sensory neurons in the nasal olfactory epithelium, which transmit signals along the olfactory tract to the primary and secondary olfactory cortices, eventually reaching the orbitofrontal cortex. Numerous studies highlight the importance of the right OFC in conscious olfactory perception.”
The team built on some of their prior research that identified abnormal activity in the OFC portion of the brain. This time around, they centered their study on neurochemical alterations in that region, focusing specifically on changes in the presence of N-acetyl aspartate (NAA), choline (Cho) and creatine (Cr). A group of 54 participants—27 with COVID-related anosmia and 27 controls—underwent MRS exams alongside Iran Recognition-Smell Identification Tests.
Compared to the control cohort, the post-COVID group displayed significantly lower levels of all three metabolites in the OFC region. The ratios of NAA/Cho and NAA/Cr also were lower in the anosmia group, while the Cho/Cr ratio was higher. NAA/Cho ratios were highly indicative of olfactory scores on the smell identification assessments, the group noted.
“The elevated Cho/Cr ratio observed in patients with persistent anosmia after six months, compared to the recovery group, likely reflects distinct pathological processes in these individuals,” the authors explained. “Choline, a marker of membrane turnover and cellular disruption, is increased in these cases, suggesting heightened membrane turnover or disruption in the orbitofrontal cortex. This persistent membrane activity may indicate ongoing repair mechanisms or chronic dysfunction within the neuronal microenvironment.”
The team suggested that Cho/Cr ratios on imaging could represent a potential biomarker for gauging the likelihood of a person recovering their sense of smell.
“The interplay between Cho and Cr highlights the complex metabolic changes underlying persistent anosmia,” they noted. “Further studies involving larger cohorts and diverse clinical settings are needed to validate the predictive value of the Cho/Cr ratio.”
In addition to her background in journalism, Hannah also has patient-facing experience in clinical settings, having spent more than 12 years working as a registered rad tech. She began covering the medical imaging industry for Innovate Healthcare in 2021.